The dimensionless ratio U?/?Lg , called Froude number, is a measure of similarity between an ocean-going ship and a scale model of the ship to be tested in a laboratory water channel. A 150 m long cargo ship is designed to run at 36 km/h, and a 1.5 m geometrically similar model is towed in a water channel to study wave resistance. What should be the towing speed in m s–1?
A ship model and its prototype
Froude number = U? /?Lg is a measure of similarity
Ship length (Ls) = 150 m
Ship speed (U?s) = 20 knots
Model length (Lm) = 1.5 m
FIND
Model towing speed (U?m)
SKETCH
For similar wave shape, the Froude number should be the same for the model and the prototype
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